NOUN (1)

1. an advocate of Gnosticism;


ADJECTIVE (2)

1. of or relating to Gnosticism;
- Example: "Gnostic writings"

2. possessing intellectual or esoteric knowledge of spiritual things;

The Collaborative International Dictionary of English v.0.48:

Gnostic \Gnos"tic\, a.
   1. Knowing; wise; shrewd. [Old Slang]
      [1913 Webster]

            I said you were a gnostic fellow.     --Sir W.
                                                  Scott.
      [1913 Webster]

   2. (Eccl. Hist.) Of or pertaining to Gnosticism or its
      adherents; as, the Gnostic heresy.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Gnostic \Gnos"tic\, n. [L. gnosticus, Gr. ? good at knowing,
   sagacious; as a n., man that claims to have a deeper wisdom,
   fr. gignw`skein to know: cf. F. gnostique. See Know.]
   (Eccl. Hist.)
   One of the so-called philosophers in the first ages of
   Christianity, who claimed a true philosophical interpretation
   of the Christian religion. Their system combined Oriental
   theology and Greek philosophy with the doctrines of
   Christianity. They held that all natures, intelligible,
   intellectual, and material, are derived from the Deity by
   successive emanations, which they called Eons.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Gnostic
    adj 1: of or relating to Gnosticism; "Gnostic writings"
    2: possessing intellectual or esoteric knowledge of spiritual
       things [ant: agnostic, agnostical]
    n 1: an advocate of Gnosticism